Energy storage device and method for detecting the occurrence of lithium plating, battery arrangement and motor vehicle

Abstract

Energy storage device with an energy storage cell (1) in the form of a lithium-ion battery with at least one electrode winding or electrode stack (2 - 6) comprising at least one anode and cathode layer (2, 3), - at least one temperature sensor (10) which is arranged at least partially inside the electrode winding or electrode stack (2 - 6) and is designed to detect a time-dependent temperature profile (T) inside the electrode winding or electrode stack (2 - 6), and - a processing unit (20) which is designed to detect a change in the slope of the time course of the temperature (T) and to infer, based on the change in the slope, a deposition of lithium ions on the at least one anode layer (2), wherein - the temperature sensor (10) has a thermopile formed from two or more thermocouples (14) connected in series, - the thermocouples are each formed from two electrical conductors (11, 12) made of different materials connected at a contact point (13), - the thermopile has two or more contact points (13, 13') at which the two electrical conductors (11, 12) made of different materials are connected to each other, and - the thermocouples (14) are arranged such that a first subset of the contact points (13) is located inside the electrode winding or electrode stack (2 - 6) and a second subset of the contact points (13') is located outside the electrode winding or electrode stack (2 - 6).

Description

[0001] The invention relates to an energy storage device and a method for detecting the occurrence of lithium plating in an energy storage cell in the form of a lithium-ion battery according to the preamble of the independent claims, as well as a corresponding battery arrangement and a corresponding motor vehicle. Lithium-ion batteries are particularly suitable for use in hybrid and electric vehicles due to their high energy densities and cell voltages compared to other battery types. However, at high currents or low temperatures, undesirable lithium deposition can occur on the anode, which is often made of graphite, instead of being intercalated between the graphite layers. This effect, also known as lithium plating, can lead to internal short circuits and result in significant losses in performance, lifespan, and safety.

[0002] The publications DE 10 2013 015 700 A1, US 2013 / 0 004 811 A1 and WO 2014 / 004 523 A1 describe battery cells that have a temperature sensor.

[0003] The object of the invention is to provide an energy storage device, a method, a battery arrangement and a motor vehicle in which the occurrence of lithium plating can be detected in a simple and reliable manner.

[0004] This task is solved by the energy storage device and the method according to the independent claims, a corresponding battery arrangement and a corresponding motor vehicle.

[0005] The energy storage device according to the invention comprises an energy storage cell, in particular in the form of a lithium-ion battery, with at least one electrode winding or electrode stack, wherein the electrode winding or electrode stack has at least one anode and cathode layer, and is characterized by at least one temperature sensor, which is arranged at least partially inside the electrode winding or electrode stack and is designed to detect a time-dependent temperature profile inside the electrode winding or electrode stack, and a processing unit, which is designed to determine a change in the slope of the time-dependent temperature profile and to infer, based on the change in the slope, a deposition of lithium ions on the at least one anode layer.The temperature sensor has a thermopile formed from two or more thermocouples connected in series, wherein the thermocouples are arranged such that a first subset of the contact points is located inside the electrode winding or electrode stack and a second subset of the contact points is located outside the electrode winding or electrode stack.

[0006] The inventive method for detecting the occurrence of lithium plating in an energy storage cell, in particular in the form of a lithium-ion battery, with at least one electrode winding or electrode stack having at least one anode and cathode layer, is characterized in that a temperature profile over time is detected inside the electrode winding or electrode stack by means of a temperature sensor arranged at least partially inside the electrode winding or electrode stack, a change in the slope of the temperature profile over time is determined, and the occurrence of lithium ion deposition on the at least one anode layer is inferred from the change in the slope.

[0007] The battery arrangement according to the invention comprises several energy storage devices according to the invention, which are preferably connected in series and / or parallel.

[0008] The motor vehicle according to the invention has an electric drive or a hybrid drive as well as an energy storage device and / or a battery arrangement according to the invention.

[0009] A motor vehicle within the meaning of the present invention is preferably a land vehicle that is not permanently guided on tracks, in particular a road vehicle, for example a passenger car, truck, bus or motorcycle, which in particular has a hybrid or electric drive.

[0010] The invention is based on the approach of detecting the temperature profile inside the energy storage cell using a temperature sensor that is at least partially located inside the energy storage cell. The temperature profile, preferably detected during the discharge and / or charging of the energy storage cell, is analyzed in a processing unit by determining the change in the slope of the temperature profile over time, for example, by calculating the first derivative of the temperature profile. Based on the determined change in the slope of the temperature profile over time, it is then possible to infer the start and / or end of lithium plating and / or whether lithium plating is already underway. Preferably, the determined change in the slope of the temperature profile over time is compared with predetermined or predefinable slope values ​​and / or slope profiles that are characteristic of lithium plating.By arranging at least one section of the temperature sensor in the area of ​​the electrodes, in particular in the area of ​​an anode, the electrode winding or electrode stack of the energy storage cell, the temperature profile relevant for the early detection of lithium plating can be determined without significant time delays and with high accuracy, so that lithium plating can be reliably detected shortly after its onset.

[0011] Overall, the invention enables the detection of lithium plating in a simple and reliable manner.

[0012] In a preferred embodiment, the processing unit is further configured to detect a change in sign in the slope of the temperature profile over time and, upon such a change, to infer the deposition of lithium ions on the at least one anode layer. For example, a change in sign of the slope of the temperature profile recorded during charging of the energy storage cell, detected at a specific time, can indicate the onset of lithium plating. Furthermore, the detection of a change in sign of the slope of the temperature profile recorded during discharging of the energy storage cell can indicate that lithium plating may have already occurred.To detect a sign change, for example, the second derivative of the recorded temperature profile can be calculated, and a conclusion can be drawn about lithium plating occurring at the point when the second derivative crosses zero. Overall, this method allows for the early and reliable detection of lithium plating that is already underway or has already occurred.

[0013] Preferably, the processing unit is configured to detect a transition from a positive to a negative temperature gradient and, upon such a transition, to indicate the deposition of lithium ions on the at least one anode layer. This allows for the early detection of lithium plating during the charging of the energy storage cell, enabling timely initiation of any necessary countermeasures.

[0014] In a preferred embodiment, the energy storage device includes a current limiting unit configured to limit the charging current during charging of the energy storage cell. The processing unit is further configured to control the current limiting unit such that the charging current is limited to a predetermined value when lithium ion deposition on the at least one anode layer is detected. Alternatively or additionally, in response to lithium plating, a short discharge pulse can be applied to remove the already deposited lithium from the anode. In this way, the onset or progression of lithium ion deposition on the anode(s) can be reliably and safely prevented, or the lithium plating can be reversed.

[0015] The temperature sensor features a thermopile formed from two or more thermocouples connected in series, each with two or more contact points where the two electrical conductor structures made of different materials are connected. Connecting multiple thermocouples in series increases the total generated thermoelectric voltage, allowing temperature changes within the cell to be detected with particularly high resolution, thus making plating detection even more reliable.

[0016] In the temperature sensor according to the invention, the thermocouples are arranged and / or configured such that a first subset of the contact points is located inside the electrode coil or stack, and a second subset of the contact points is located outside the electrode coil or stack. A thermoelectric voltage is established at both ends of the thermopile, which depends on the difference between the temperature in the region of the contact points located outside the coil or stack and the temperature in the region of the contact points located inside the coil or stack. Preferably, by measuring the absolute temperature in the region of the contact points located outside the coil or stack, for example by means of another temperature sensor located there, the absolute temperature inside the coil or stack can be determined from the voltage-temperature characteristic of the thermopile.This allows for a particularly reliable conclusion to be drawn about possible plating based on the absolute temperature determined in this way or the time course of the absolute temperature.

[0017] Furthermore, it is preferred that the electrical conductor structures of the series-connected thermocouples have a meandering shape. In another preferred embodiment, the temperature sensor has a flexible substrate onto which the electrical conductor structures are applied. A thin polyimide film, for example, can serve as the substrate. The thermocouples are preferably applied to the preferably thin substrate using thin-film technology, resulting in a very low overall thickness for the temperature sensor, allowing it to be easily integrated into the electrode winding or stack.

[0018] It is also preferred that the electrical conductor structures consist of a nickel alloy and a chromium-nickel alloy. However, the thermocouples can also be implemented using conductor structures made of other material combinations, such as iron and copper-nickel alloy or platinum and platinum-rhodium alloy.

[0019] Preferably, the thermopile is arranged on and / or in contact with at least one anode layer of the electrode winding or stack. The temperature sensor is then preferably located between an anode layer and a separator layer adjacent to the anode layer. This allows for particularly reliable and early detection of temperature changes caused by potential plating, so that any countermeasures, such as limiting and / or reducing the charging current, can be initiated in a timely manner to prevent negative effects of plating on the cell's function. This ensures reliable and safe operation of the energy storage cell, especially at low operating temperatures where plating is more prevalent. The same applies in the case of fast charging of the cell, where the occurrence of plating is promoted by high charging currents.

[0020] Further features, advantages, and applications of the invention will become apparent from the following description in conjunction with the figures. The figures show: Fig. 1. An example of a temperature sensor in front view; Fig. 2 Another example of a temperature sensor in front view; Fig. 3. An example of an energy storage device in a cross-sectional view; and Fig. 4 An example of a temperature profile recorded over time by a temperature sensor inside an energy storage cell.

[0021] Fig. Figure 1 shows an example of a temperature sensor 10 with a preferably mechanically flexible substrate 15, for example a polyimide film, onto which several first structures 11 made of an electrically conductive first material and several second structures 12 made of an electrically conductive second material are applied. The structures 11 and 12 can, for example, be applied to the substrate 15 by means of physical or chemical vapor deposition (PVD or CVD).

[0022] The electrically conductive first material of the first structures 11 can, for example, be a nickel alloy, such as Alumel with 95% nickel, 2% manganese, 2% aluminum, and 1% silicon. The electrically conductive second material of the second structures 12 can, for example, be a nickel-chromium alloy, such as Chromel with approximately 90% nickel and 10% chromium. By establishing an electrical contact 13 between the first and second structures 11 and 12, a so-called thermocouple 14 is obtained, which, due to the combination of the first and second materials chosen in this example, is of type K. Alternatively, it is also possible to realize thermocouples 14 from other material combinations, such as type J thermocouples made from a combination of iron and a copper-nickel alloy, or type S thermocouples made from a platinum-rhodium alloy and platinum.

[0023] In the present example, the first and second structures 11 and 12 are each shaped like steps and arranged and electrically connected to each other in such a way that they form a so-called thermopile with a meandering overall structure, in which a first structure 11 and a second structure 12 alternate. As a result, first contact points 13 are located at the lower end of the meandering course of the overall structure, whereas second contact points 13' are located at the upper end of the meandering course of the overall structure.

[0024] If the lower region of the temperature sensor 10, with its first contact points 13, is inserted into the interior of an electrode winding or electrode stack of an energy storage cell, and the second contact points in the upper region of the temperature sensor 10 are located outside the electrode winding or electrode stack, then different thermoelectric voltages are established at the first contact points 13 than at the second contact points 13' when temperatures T1 and T2 are different outside and inside the energy storage cell. Depending on the temperature difference T1-T2 between the outside and the inside of the electrode winding or stack, different thermoelectric voltages are measured at electrical contact elements 16 at the two ends of the thermopile.

[0025] Preferably, the magnitude of the resulting thermoelectric voltage at the contact elements 16 can be adjusted by varying the number of thermocouples 14 connected in series. For example, at a specific temperature difference T1-T2, a temperature sensor 10 with a total of ten thermocouples 14 will produce twice the thermoelectric voltage at the contact elements 16 compared to a temperature sensor 10 with only five thermocouples 14. By selecting a sufficiently high number of thermocouples 14 connected in series, the sensitivity of the temperature sensor 10 can be specifically increased to enable particularly accurate detection of the temperature profile in the energy storage cell.

[0026] Fig. Figure 2 shows another example of a temperature sensor 10, in which the first and second structures 11, 12 applied to a substrate 15 are covered by a cover layer 17. As with the substrate 15, a polyimide film can be used as the cover layer 17.

[0027] Preferably, the covering layer 17 is designed such that the electrical contact elements 16 at the beginning and end of the series-connected thermocouples are not covered, allowing for easy contact. Otherwise, the descriptions in connection with the [reference to be added] apply. Fig. 1. This corresponds to the example shown.

[0028] Fig. Figure 3 shows an example of an energy storage device with an energy storage cell 1 in the form of a lithium-ion battery with multiple anode layers 2, cathode layers 3, separator layers 4 arranged between the anode and cathode layers 2 and 3, anode current collectors 5 provided on the anode layers 2, and cathode current collectors 6 provided on the cathode layers 3. The one or more anode layers 2 are preferably graphite layers. Depending on the design of the energy storage cell 1, the aforementioned layers 2 to 6 can, as indicated in the illustrated example, be arranged essentially parallel to each other, forming a so-called electrode stack. Alternatively, it is also possible for a sequence of layers consisting of anode 2, separator 4, and cathode 3, possibly together with corresponding current collectors 5 and 6, to be wound together to form a so-called electrode coil.

[0029] The energy storage cell 1 further comprises an electrolyte (not shown), which is located, in particular, in cavities of the separator layers 4 provided between the anode and cathode layers 2, 3. Preferably, the electrolyte is an electrolyte liquid consisting of lithium salts dissolved in a solvent, such as LiPF6. Alternatively, it can also be lithium phosphate nitride (LiPO4N) or a polymer of polyvinylidene fluoride (PVDF) or polyvinylidene fluoride hexafluoropropene (PVDF-HFP).

[0030] A temperature sensor 10 is arranged on an anode layer 2 of the energy storage cell 1, which preferably corresponds to the one described above in connection with the Fig. 1 and Fig. This corresponds to the temperature sensor described in Figure 2. In the representation chosen here, the temperature sensor 10 is shown in cross-section, i.e., the meandering course of the first and second structures 11 and 12 connected in series (see Figure 2). Fig. 1) runs perpendicular to the plane of the drawing or essentially parallel to the anode layer 2, to which the temperature sensor 10 is attached.

[0031] As already mentioned in connection with Fig. As explained in Figure 1, only a lower section of the temperature sensor 10 is located within the energy storage cell 1, i.e., in this case between an anode layer 2 on the one hand and a separator layer 4 on the other, whereas an upper section of the temperature sensor 10 protrudes from the energy storage cell 1, so that the first contact points 13 are located inside and the second contact points 13' are located outside the cell. The upper region of the temperature sensor 10 can preferably be located in a so-called gas space at the upper end of the electrode winding or stack and may optionally be located within a housing enclosing the electrode winding or stack. Since heat transfer from the electrode winding or stack into the gas space is comparatively small or even negligible, the temperature T1 there changes only slightly or hardly at all during the charging or discharging of the energy storage cell 1.In contrast, the temperature T2 inside the cell, and thus also in the area of ​​the lower end of the temperature sensor 10, will change comparatively strongly, so that correspondingly high thermoelectric voltages are present at the contact elements 16 of the temperature sensor 10, which are tapped there and supplied to a processing unit 20.

[0032] In processing unit 20, the temporal profile of the resulting thermoelectric voltage is recorded, processed, and evaluated by, among other things, determining the slope of the obtained thermoelectric voltage over time, for example, by calculating the first derivative of the thermoelectric voltage, and preferably taking into account the current operating state, such as discharging or charging, of the energy storage cell 1. In particular, certain temporal changes in the slope of the thermoelectric voltage profile can be used to infer lithium plating, i.e., an undesired deposition of lithium ions on the anode layer 2, and / or the onset of lithium plating.

[0033] If the evaluation of the thermoelectric voltage profile over time in the processing unit 20 indicates that lithium plating is imminent or has already begun, a current limiting unit 30 is controlled by the processing unit 20 in such a way that it reduces or limits the charging current accordingly, in order to avoid, in particular, internal short circuits in the cell as a possible consequence of undesirable lithium deposits on the anode 2.

[0034] Fig. Figure 4 shows an example of a temperature T profile recorded by a temperature sensor 10 inside an energy storage cell 1 during a charging process L and a subsequent discharging process E. The temperature T plotted over time t corresponds essentially to the thermoelectric voltage generated by the temperature sensor 10 due to a temperature difference between the section of the temperature sensor 10 located outside the electrode winding or stack and the section of the temperature sensor 10 located at the anode 2 of the electrode winding or stack.

[0035] How Fig. As can be seen in Figure 4, in the example shown, the temperature T initially rises during the charging process L and then falls from time t onwards. P This means that the temperature T initially shows a positive increase over time from time t onwards. Ptransitions into a negative slope. Surprisingly, it was found that time t corresponds to this. P in the region of the transition from a positive slope to a negative slope of the temperature profile at the time of the start of lithium plating on the anode(s) 2 of the energy storage cell 1. By the preferred arrangement of the temperature sensor 10 directly on at least one of the anodes 2 (see Fig. 3) This ensures that this change in the temperature profile is detected without any significant time delay, thus enabling early detection of incipient plating in order to prevent the plating from progressing and any short circuits in the cell, for example by reducing and / or limiting the charging current during charging L.

[0036] Furthermore, it is possible to determine the temperature T during the discharge process E from time t onwards. ELto determine whether lithium ions have been deposited on the anode layer(s) 2 of the energy storage cell 1. As from Fig. As can be seen in section 4, the temperature inside the cell rises after time t. EL The discharge process E begins with a brief, initially positive slope, which, after exceeding a maximum, transitions into a comparatively steep decline with a negative slope. This indicates the detachment of lithium ions previously deposited on anode 2. Such a transition during the discharge process E of energy storage cell 1 can thus reveal any plating that may have already occurred. Reference symbol list 1 energy storage cell 2 Anode, anode layer 3 Cathode, cathode layer 4 Separator layer 5 anode drains 6 cathode separators 10 Temperature sensor 11 first structure 12 second structure 13 Contact point within the energy storage cell 13' Contact point outside the energy storage cell 14 Thermocouple 15 substrate 16 electrical contact element 17 Cover layer 20 processing units 30 Current limiting unit E Unloading process L Charging process Temperature t time t P Time of commencement of plating t EL Time of the switch from the charging to the discharging process T1 Temperature outside the energy storage cell T2 temperature inside the energy storage cell

Claims

[1] Energy storage device with an energy storage cell (1) in the form of a lithium-ion battery with at least one electrode winding or electrode stack (2 - 6) comprising at least one anode and cathode layer (2, 3) - at least one temperature sensor (10) which is arranged at least partially inside the electrode winding or electrode stack (2 - 6) and is designed to detect a time course of a temperature (T) inside the electrode winding or electrode stack (2 - 6), and - a processing unit (20) which is designed to detect a change in the slope of the temperature (T) over time and to infer, based on the change in slope, a deposition of lithium ions on the at least one anode layer (2), wherein - the temperature sensor (10) has a thermopile formed from two or more thermocouples (14) connected in series, - the thermocouples are each formed from two electrical conductors (11, 12) made of different materials connected at a contact point (13), - the thermopile has two or more contact points (13, 13') at which the two electrical conductors (11, 12) made of different materials are connected to each other, and - the thermocouples (14) are arranged such that a first subset of the contact points (13) is located inside the electrode winding or electrode stack (2 - 6) and a second subset of the contact points (13') is located outside the electrode winding or electrode stack (2 - 6). [2] Energy storage device according to claim 1, wherein the processing unit (20) is further configured to - to determine a transition from a positive slope in the time course of the temperature (T) to a negative slope in the time course of the temperature (T) and - to conclude that a transition from a positive slope to a negative slope occurs, indicating a deposition of lithium ions on the at least one anode layer (2). [3] Energy storage device according to one of the preceding claims with a current limiting unit (30) which is configured to limit a charging current when charging the energy storage cell (1), wherein the processing unit (20) is further configured to control the current limiting unit (30) in such a way that the charging current is limited by the current limiting unit (30) to a predetermined charging current when a deposition of lithium ions on the at least one anode layer (2) has been inferred. [4] Energy storage device according to one of the preceding claims, wherein the electrical conductors (11, 12) of the series-connected thermocouples (14) have a meandering shape. [5] Energy storage device according to one of the preceding claims, wherein the temperature sensor (10) has a flexible substrate (15) on which the electrical conductors (11, 12) are applied. [6] Energy storage device according to one of the preceding claims, wherein the electrical conductors (11, 12) comprise a nickel alloy and a chromium-nickel alloy. [7] Energy storage device according to one of the preceding claims, wherein the thermopile is arranged and / or is in contact with at least one anode layer (2) of the electrode winding or electrode stack (2 - 6). [8] Battery arrangement with multiple energy storage devices according to one of the preceding claims. [9] Motor vehicle with an electric drive or a hybrid drive and a battery arrangement according to the preceding claim. [10] Method for detecting the occurrence of lithium plating in an energy storage cell in the form of a lithium-ion battery with at least one electrode winding or electrode stack (2 - 6) having at least one anode and cathode layer (2, 3), comprising the steps - Detecting a time course of a temperature (T) inside the electrode winding or electrode stack (2 - 6) by means of a temperature sensor (10) arranged at least partially inside the electrode winding or electrode stack (2 - 6), - Determination of a change in the slope of the time course of temperature (T) and - Inferring the occurrence of a lithium ion deposit on the at least one anode layer based on the change in slope, wherein - the temperature sensor (10) has a thermopile formed from two or more thermocouples (14) connected in series, - the thermocouples are each formed from two electrical conductors (11, 12) made of different materials connected at a contact point (13), - the thermopile has two or more contact points (13, 13') at which the two electrical conductors (11, 12) made of different materials are connected to each other, and - the thermocouples (14) are arranged such that a first subset of the contact points (13) is located inside the electrode winding or electrode stack (2 - 6) and a second subset of the contact points (13') is located outside the electrode winding or electrode stack (2 - 6).

Images